Silicone rubbers find frequent use as coatings for electrical wire and cable as consequence of their excellent heat resistance, excellent cold resistance, excellent resistance to aging, excellent electrical properties, and the like. 2,4-Dichlorobenzoyl peroxide has in the past been employed as a curing agent for effecting cure of the silicone rubber compositions employed as cable and wire coatings. However, silicone rubber compositions containing this organoperoxide have been associated with a number of problems, i.e., the generation of unpleasant odor during cure, the generation of stickiness, or tack on the molding surface post-cure, and blooming onto the surface of the silicone rubber molding post-cure. Blooming is the gradual outmigration of degradation products originating from the curing agent and presents as a whitening of the molding surface. A great deal of research has been performed to date in order to solve these problems. For example, Japanese Patent Application Laid Open (Kokai or Unexamined) Number Sho 54-48870 (48,870/1979) teaches a method for preparing low-surface-tack silicone rubber moldings through the use of bis(2,4-dichlorobenzoyl)peroxide and di-tert-butyl peroxide as the curing agent. However, this method is not fully satisfactory because it does not completely suppress tack on the molding surface or the unpleasant odor generated during cure. Japanese Patent Application Laid Open (Kokai or Unexamined) Number Sho 59-18758 (18,758/1984) teaches a method that uses bis(ortho-methylbenzoyl)peroxide as the silicone rubber composition curing agent. Neither the above-described blooming nor unpleasant odor generation occur with this method. In addition, Japanese Patent Application Laid Open (Kokai or Unexamined) Number Sho 62-185750 (185,750/1987) proposes a method that solves the above-described problems through the use of bis(para-methylbenzoyl)peroxide as the silicone rubber composition curing agent. However, the silicone rubber moldings produced by the thermosetting of a silicone rubber composition prepared according to the former method (use of bis(ortho-methylbenzoyl)peroxide) have a yellowish tint (yellowing), while the silicone rubber composition prepared according to the latter method (use of bis(para-methylbenzoyl)peroxide) suffers from a slow cure rate and a pronounced tendency to foam during curing with the production of microscopic bubbles (voids).
In particular, a fatal drawback of the above-described silicone rubber compositions that use methyl-substituted benzoyl peroxide as curing agent is that they afford silicone rubber coatings with a substantially diminished flame resistance. The object of the present invention is to provide an EWC silicone rubber composition and in particular to provide a highly flame-retardant EWC silicone rubber composition.